Place sausage, potatoes, onion, bell pepper, and carrots in a large roasting pan, being careful not to crowd. Sprinkle with olive oil, garlic, rosemary, and red pepper flakes, and toss to coat. Sprinkle with coarsely ground black pepper. Place in oven and roast for 30 minutes, stirring occasionally, until potatoes are tender. Remove from oven, season with sea salt and additional pepper, and drizzle with additional olive oil before serving, if desired.